not using birth control (women), medications or medical conditions that counterindicated naltrexone treatment. A subset of participants provided consent for DNA collection and represents the current sample. As genotyping in this study began about 12 months after recruitment started, the sample sizes for the DRD4 and OPRM1 analyses are n = 112 and n = 105, respectively. See Table 1 for participant characteristics and genotype comparisons. To assess for potential selection bias due to the fact that only a subset of patients participated in the DNA collection, consenters (n = 112) and non-consenters (n = 64; 38 who could not be contacted; 26 who refused consent) were compared on the baseline characteristics.
